This invention relates to a hydraulic controller in hydraulic valves used in construction equipments, and more particularly to a hydraulic controller with low pressure loss, superior responsibility, high stability, and in complex-operability.
The hydraulic control valve as shown in FIG. 4 has been known as hydraulic controllers.
Thus hydraulic control valve as illustrated in FIG. 4 has the following elements. A switching spool 12 is accommodated in a valve body 10. A compressed oil is supplied from a supplying passage 14 of a hydraulic pump to a cylinder port 16a or 16b. In connection with a relative movement of the switching spool 12 to the valve body 10, a passage from the supplying passage 14 to an oil chamber 18 is opened, whereby, the compressed oil having entered into the oil chamber 18, is reached to an oil chamber 20, so that when the switching spool 12 is in a neutral position, a plunger 24 is moved upwardly, which blocks passages 22, 22 extending between the oil chamber 20 and a cylinder port 16a or 16b positioned in downstream side of the oil chamber 20, before the pressured oil enters into the passages, 22, 22 and then into the cylinder port 16a or 16b.
In a back chamber 25 of the plunger 24, when the compressed oil applying onto plunger 24 is passed from the oil chamber 20 to the passage 22, almost constant pressure drop appears such as to allow the plunger 24 to act as a pressure compensation means as well as the plunger 24 to exhibit a certain operation. For these purposes, a spring 26 is provided to apply its elastic force to the plunger 24, whereby the oil chamber 20 is shut from the passage 22. If, however, this spring 26 is not provided, the plunger 24 has no stable balanced position, thereby making it difficult to stabilize the pressure compensation function.
The back chamber 25 of the plunger 24 is connected to the outside through a communication passage 28 which may optionally be further connected to the tank circuit 29 trough the throttle.
For the well-known hydraulic control valves, other than the above, in order to supply the compressed oil from the supplying passage of the hydraulic pump, a movable member is provided as a pressure compensation valve on the passage of the compressed oil, and further in order to cause a constant pressure reduction in the upstream and downstream sides of the movable member, the spring force is designed to work on the movable member in such a way to close the passage to the cylinder port from the supplying passage.
However, there had remained various problems with the conventional hydraulic control valves, which should have to be solved.
In the prior art mentioned above, the pressure compensation valves are provided between the supplying passage and the cylinder port, and the pressure compensation valves are free from a compressed fluid action applied with the spring force such as to close the supplying passage to the a cylinder port from the hydraulic pump. Therefore, in order to operate the switching spool for causing the compressed oil to be flowed into the cylinder port, it is necessary that the pressure compensation valve is kept open against the spring force. In order to provide the function as the pressure compensation valve, it is also necessary that the spring force is not so faint, whereby the pressure loss corresponding the spring force is caused, making it difficult save energy.
Furthermore, in the hydraulic control valve as shown in FIG. 4, the back chamber of the plunger is connected to the tank circuit through the throttle. When the switching spool is in a non-operating state, the hydraulic control valve is kept closing the passage to the cylinder port from the supplying passage of the hydraulic pump. If the hydraulic control valve is used in a cold district, then the hydraulic oil has an extremely high viscosity. For this reason, if the high viscosity hydraulic oil is used for quick start, then the hydraulic oil in the valve chamber of the hydraulic control valve is exhausted to the outside through the throttle.
This exhaust takes some time during which the plunger remains in position, whereby the movement of the plunger as the pressure compensation valve for opening the upstream and downstream passages is likely to be delayed in response.
In this case, this response may be improved by widening the opening degree of the throttle. In order to but in order to keep the pressure compensation valve in good performance, it is however necessary to increase the quantity of the discharged oil from the throttle. This may raise another problem in difficulty to save energy for the whole system.
Furthermore, in concurrent operations of two spools, all of the pressure compensation valves must be equilibrated individually in the respective neutral positions between the closed and opened positions. Accordingly, these values tend to be influenced mutually, and thus it is required to consider the safety enough well.
In the prior art, a flow rate regulating device is connected between a switching valve and a cylinder port, that is, an actuator is connected to a hydraulic control device.
In this case, by limit the supply of the oil from a hydraulic pump to an actuator, namely by the flow rate control is made by the meter-in control. When the hydraulic control unit is used in the construction equipment, the following problem is raised. Though the load reduced with empty weight should be under the meter-out control, the degree of opening on the side of the meter-in control is limited as described above, whereby a cavitation is formed due; to insufficient supply of the compressed oil to the actuator, thereby making difficult a smooth operation of the load.
Upon repeated earnest studies and investigations the inventor could confirm the following facts.